For the 3DS, head here (if you have a system on FW 9.3 or more recent): http://smealum.github.io/3ds/
If your 3DS is on 9.2 or lower, go here to install RXtools (if you have an O3DS) or here (if you have a N3DS).
On PSVita, I don't really know (since I don't have one), but I think you can go here to get started.
And on PS4, afaik, there is no hack at the moment (except some kind of browser exploit that can launch Homebrew on old firmware), if you don't count the NAND copying thing.